Abstract:
The amplitude and phase response of individual peripheral auditory organs was measured in goldfish using a noninvasive ultrasonic measurement system. Individual fish were anesthetized and suspended within a low-frequency acoustic field generated by two underwater sound projectors coupled to the ends of a 14-m-long, water-filled acrylic tube. Active control was used to synthesize a plane traveling wave within the tube at frequencies down to 12.5 Hz. Simultaneously, the fish was insonified by a continuous wave ultrasonic source operating at 15 MHz. A separate ultrasonic transducer acted as receiver. Motion of the target due to the low-frequency acoustic field caused the received signal to be phase modulated. Target amplitude information was obtained directly from the receiver output using a high-frequency spectrum analyzer; phase information required demodulation of the received signal. A motorized positioning system allowed the fish to be moved relative to the measurement system so that different organs could be examined. The spatial resolution of the measurement system was about 0.2 mm. Using this system, the responses of the goldfish swimbladder, Weberian ossicles, and otoliths have been measured at frequencies down to 12.5 Hz and compared to existing models. [Work supported by ONR Grant No. N00014-94-1-0337.]